Telephone system



D. A. CHRISTIAN ET AL TELEPHONE SYSTEM 2 Sheets-Sheet 1 Feb. 28, 1933.

Filed June 9, 1930 IHII [1m Dauid Edam [PETE-T Edmund William Palmer Feb. 28, 1933. I D. A. CHRISTIAN E-T AL 1,899,014

TELEPHONE SYSTEM Filed June 9, 1930 2 Sheets-Sheet 2 Wei 7 *llllllill IH I 1H KMWA IITUEFL BPS David Edam EHFEIEH E dmund Mlliam Falme'r Patented Feb. 28, 1933 PATENT orrlce pnvrn AJQAM ,c-Hmsrrmn nn np vrunn WILLIAM PALMER, or LONDON, ENGLAND,

- A SIGNOB S 9 SIEME 5339 331 3 8 COMPA L MIT D F NDON ENGLA TELEPHONE SYSTEM Application filed lune9, 1930, Serial No. 459,864, and in GreatBritain July 1, 1929.

The present invention relates to the control of alternating and /or pulsating currents in electrical circuits.

It is -,W6ll known that so-called rectifying devices possess the property of offering a low resistance to currents flowing in one direction whilst offering a high resistance to currents flowing in the opposite direction, thereby substantially preventing current flow in 1 that opposite direction.

According to this invention alternating or pulsating current is permitted to flow from acommon circuit to a (branch circuit or circuits and is prevented from flowing in an other branchcircuit or circuits by superimposing the alternating or pulsating current on -a steady direct current without altering its polarity and connecting rectifiers in the branch circuits :to permit the flow of current 1 or not according to the direction of flowofthe direct current;

In carrying .out this featureeaeh branch may be furnished with a rectifying device and a, steady potential is applied to the common part of the circuit. The rectifying devicesare so connected that whilstsome'oii'er a low resistance to current-flow from the common part of the circuit in one direction, others olier a'low resistance to current flowing-in the opposite direction. An alternating Speech currents are transmitted by modulating a steady current flowing in a circuit and therefore pass in the branch in which the rectifying device offers a low resistance to the steady current but have no elfect on apparatusconnected in the other branch. As the variation in the current in the circuit due to speech is small compared with the normal value of the steady current itself, the whole of the speech waves will pass the rectifying device with consequent full reproduction in the telephone receiver.

In a telephone vor signalling system the steady potential may be applied at a control point and may provide the current necessary for speech or transmission of signals.

In a further feature of the invention, discriminating arrangements are provided for identifying a branch station at a control point and for the connection of signalling current to the common connecting linefor switching points in opposite directions so that a common connecting link may be em:- ployed to connect the source of signalling current in the appropriate direction. Where automatic switching means are used, disoft crimination may be effected in a similar manner, the signal receiving apparatus operated effecting the connection of signalling current. In the case of calls to a branch station from the control point, the switches which make connection with the connecting line may provide for the correct connection of signalling current. The calling of branch stations from the control point may be effected over different wires as in the case of calls from a branch station.

Reference will now be had to the accompanying drawings which show applications e invention to party line telephone systems.

In the drawings Fig. 1 shows diagrammatically a two-party line connected to a manuall Y operated telephone exchange, and Fig. 2 s ows a similar party line connected to an automatic telephone exchange.

In Fig. 1 the instruments of the two parties are designated'X and Y and are shown on the right hand side of the figure connected by a common line a b to the exchange. The termination of the line at the exchange is shown on the left hand side of the figure. The line is rovided with nmltiple and answering jac s and line relays for each subscriber and a single cut-ofl relay is provided for the line, contacts of this latter relay being included in the line relay circuits in the usual manner.

- The line relays designated LX and LY for the X and Y parties, respectively, are connected between the negative pole of battery and one of the line wires, relay LX being connected to wire b and relay LY to wire a. Inorder that a standard cord may be used a cross is inserted in-the connection of the jacks associated with one of the two parties on the line so that the speaking battery is connected to the line with opposite polarities accplrding to the party to be communicated wit At a subscribers instrument the receiver, transmitter, induction coil and condenser are connected in the usual manner, but the bell instead of being bridged in series with the condenser across the line wires is connected in series with the condenser between one line wire and earth. The switch hook performs the usual function. At each instrument is a rectifier RX or RY, which is of comparatively low resistance to current flow in one direction and of comparatively high resistance to current flow in the other direction and isconnected in one of the line wires at each instrument. The direction of current flow for which the rectifier ofiers a low resistance is indicated by the arrow head. At the X partys instrument the rectifier is connected in the a wire and at the Y partys instrument the rectifier is connected in the 6 wire. A calling key is provided to shortcircuit the condenser and connect earth over the bell coils to one of the line wires for calling purposes, the line wire being that to which the particular subscribers line is connected at the exchange. At the X instrument the rectifier is designated RX, the bell CX and the calling key KX, and at the Y instrument these parts are designated RY, CY and KY, respectively.

To make a call subscriber X removes his receiver and presses his key KX thereby connecting earth over the coils of his bell OX, the bwire, contact col, relay LX to the earthed battery at the exchange. Relay LX operates and lamp L1 is lit on the closure of contact 1x1 and the operator seeing this plu s into the answering jack J XA. The cut-0% relay CO operates over the sleeve circuit and disconnects the two line relays LX and LY at contacts 001 and 002 and as the positive pole of batter is connected to the tip of the plug current ows over wire a through the rectifier RX and the X partys instrument, the b wire, the ring of the plug to the negative pole of the battery. Speech currents being'transmitted by modulating a steady current and in this case by modulating current flowing in the circuit and in the direction described, pass through the rectifier and conversation between the operator and the X party can take place. The rectifier RY offers a high resistance to current flowing in the direction described and speech between the exchange and party X cannot, therefore, be heard by party Y. Closure of key KY during the progress of a call between the exchange and party X will not interrupt the call as earth will be connected thereby over the high impedance of bell (/Y to wire a and as the positive pole of the exchange battery is earthed, will not affect the potential applied to rectifier RX.

The subscriber having the instrument designated Y calls the exchange in a similar manner, the callin current flowing over the a wire and operating relay LY. To answer this call the operator plugs into the answering jack associated with lamp L2, lit consequent on the'operation of relay LY and the positive pole of battery is connected over the tip of the plug and the b wire, the jumpers connecting the multiple with the line being crossed, and the rectifier RY presenting only a low resistance to current in this direction, conversation may be had with subscriber Y.

From the above it will be clear without further detailed explanation how a call to either party on the party line may be set up to the exclusion of the other party.

When the operator inserts a plug into a multiple jack, say the jack JY, the current flow over the line is in a direction such that it flows through rectifier RY but not RX. To call the Y party the operator throws her ringing key which applies ringing current between the a wire and earth and bell CY is rung. The speech currents being a modula- L sented -by contacts D, are provided. Thedia'l is connected in a different line wire at each instrument on the party line. On the right hand side of the drawing is shown a linebattery in selectors in the other group is re versed so that connection may be had with the other party. Final selectors designated F1 and F2 are shown,-therc being a cross in the connections to the wipers F2 in order to reverse-the direction of battery feed to the called party line.

The linesw-itch is provided with two battery connected line relays LX and LY, con- -nectedone to each wire of the party line over contacts of the test relay T. As regards the bank contacts of the lineswitch the connections to these are duplicated, an outlet being connected symmetrically to two sets of contacts in the bank, one in the early part and one in the laterpart. For instance; it there are ten. sets of contacts and five outlets, the first outlet would be connected to contacts 1 and '6, the second to contacts 2 and 7 and so on, there being a normalcontact the commencement of the bank on which the, wipers rest when not in use. The connections to the bank contacts are .such that current to the calling line from the selector taken into'use is fed in opposite directions over the contacts in tie two parts of the bank in order that current may flow in the instrument circuit of the calling partyonly and not'in the other instrument, the permission or prevention of current flow in the instrument .cir-

cuits being determined by the rectifiers BX and RY. In, order that-a selector shall be taken into use over a route which w ll feed current in the required direction, the test circuit includes contacts of the two line =resla-ys connected to two segments wiped by a wiper of the lineswitc'h, the segments correspondin to the two sets of symmetrically arranged contacts in the banks giving access to a selector. The switch is rotated by means of magnet DM under the action of an interrupter. Current-is ted to the called line over the windings A of the selector impulse relay.

lVhen a subscriber on the party line makes a call, one ofthe line relays is operated and the line-switch moves oil in-search of a free selector, but owing to the separate segments referred to, a selector can only be seized over a route which will feed current in the required direction. Assuming subscriber Y to make a call he lit-ts his receiver and presses the calling key KY-thereby closing a circuit from earth over the coils of his instrument bell CY, d-ial contacts iD, wire a, contact $2 of test relay T, line relay LYto battery. Relay LY operates and at contact Zg l closes a circuit ove back contact $1 for magnet DM which-operates and rotates the wipers over the bank contacts by means of the interrupt-er connected in its circuit. The test for a tree outlet is battery on the test bank contact and the circuit of the test relay is prepared atcontact Zy2. lVhen the line switch is stepped from normal, the magnet circuit is earthed over the homing segment and wiper independently or" contact Zg l. The test circuit cannot be completed it a free outlet is encountered in the early part of the bank as the test relay is disconnected at wiper Z. lVhen however, the wipers are stepped on to the first contacts in the later part of the bank, wiper Z is earthed over the segment corresponding to contacts in the" bank to battery. Contact t1 changes over,

opens the circuit of magnet DM and short circuits the high resistance winding of the test relay to bring the test wiper to substan tially earth potential for engaging the outlet. Contacts t2 and t3 disconnect the line relays and switch the line through to the selector S. Dialling tone is given and current is now fed to the line over impulse relay A 7 as follows: earthed positive pole of battery, relay A, contact in later part of bank of wiper l3, wiper B, contact t3, wire 5, rectirtier RY, Y subscriberls instrument, dial contact D, wire a, contact t2, wiper A, contact in later part of bank, relay A to negative pole of battery. The subscriber releases his call key and'may now dial the wanted number by means of his dial, producing interruptions in the above traced circuit of relay A which responds to the impulses dialled.

When the connection is set up conversation takes place in the normalmanner but it cannot be heard by subscriber X as there will be no current flow through his instrument owing totherectifier RX acting as a high resistance to current flow in the direction above traced. It will be obvious that if subscriber X calls,

a similar operation of the .lineswitch will be brought about, a selector being taken into use over the early part of the bank owing to the connection of the test relay T over the first segment and contact Z402, and the selector will feed current of polarity positive on wire a and ne ative on wire I) so as to flow throu h rectifier X and not through RY. At t e end of the call the test relay is released from the selector in the usual manner and at contact t1 closes a homing circuit by which the lincswitch is rotated to its normal position where the homing circuit is broken at the homing wiper.

As regards incoming calls, test is made over the final selector test relay (not shown), test wiper and bank contact, normal contact and test wiper of the lineswitch, windings of relay T, normal contact and homing wiper to earth. Relay T operates to prevent rotation of the lineswitch and cuts oil the line relays. If the selector F1 is one in the group for calls to X parties positive pole of battery for feeding current to the called subscriber will be connected directly to wire a while in selector F2- of the group used for Y party calls positive pole of battery is connected over the cross in the connections to the final selector wipers to wire I). The subscribers bell is rung by the connection of ringing current at the final selector between a line wire and earth. The battery feed and ringing connections in the final selectors are the same in the two groups of final selectors, the ringing current being applied to the appropriate wire by the direct or crossed connection to the final selector wipers.

What is claimed is:

1. In a telephone system, two stations connected to a common line, means for establishing a talking connection with the subscriber at one of said stations, and means comprising a rectifier at the second station for preventing the subscriber thcreat from interfering with said talking connection.

2. In a telephone system, a central oflice, two stations, a common line interconnecting said central oflice and said stations, means for applying battery to said common line at said central ollioe, and means dependent on the olarity of said battery for establishing a tal ing path between said central oflice and one of said stations to the exclusion of the other.

3. In a telephone system, a central ofiice, a common line, two stations connected to said common line, answering and multiple jacks at said central office for each of said stations, means at said stations for signalling the operator at said central ofiice, means for establishing a talking connection between the operator at said central oflice and one of said stations, and a rectifier for preventing the other of said stations from listening in on said talking connection.

4. In a telephone system, a central ofiice, two stations, a common line interconnecting said stations with said central ofiice, means at said central ofliee for connecting a steady potential to said common line, and means at said stations for permitting one of said stations but not the other to use the line, the station to use the line being determined by the polarity of said steady potential.

5. The method of allowing entry of alternating or pulsating current from a common circuit into a branch circuit or circuits and barring entry into another branch circuit or circuits, which consists in applying a steady direct current to the common circuit, in superimposing the alternating or pulsating current thereon, and in barring or permltting the entry of the resultant current into the branch circuit or circuits dependent on the direction of flow of the direct current.

6. In a telephone system, a central olfice, two stations, a common two-wire line interconnecting said central ofiice and said stations, means at the central oliice for transmitting a calling signal over said line in a circuit including one wire of said line and ground, a different line wire being used for signalling each of said stations, means at the central ofiice for applying potential to said line, and rectifiers connected at each of said stations for permitting the subscriber at either of said stations to respond to said calling signal to the exclusion of the other dependent on the polarity of said potential:

7. In a telephone system, two stations, :1 central office, a common two-wire line interconnecting said central office and said stations, a set of jacks for each of said stations terminating said common line at said central ofiice, the termination of said common line at one of said sets of jacks being reversed as regards said line wires, means at said central ofiice for ap lying current to said line in either direction d ependent on the jack used, and rectifiers connected in opposite sides of said line at said stations to permit either of said stations to use the line to the exclusion of the other dependent on the direction of current flow in said line.

8. In an automatic telephone exchange, a line switch having two line relays, a trunk leading to a selector, said line switch having access to said trunk in two sections of its bank, the trunk being reversed in one of said sections, two stations connected to a common line terminating in said line switch, means responsive to the initiation of a call at either one of said stations for operating the corresponding one of said line relays, the line relay operated determining over which section of said bank said line switch will search for said trunk, and means at each of said stations for preventing a subscriber at the other station from listening in on said call.

9. In a party line lock-out system, two stations connected to a common two-wire line, the line wires terminating one of said stations being reversed as regards the line wires terminating in said other station, a rectifier connected in one of said line wires at one of said stations, a rectifier connected in the other of said line wires at said other station, a central ofiice, means responsive to the initiation of a call by either one of said stations for connecting a positive potential to one of said line wires, the station initiating the call determining the line wire the positive potential will be connected to, said rectifiers permitting one of said stations and preventing the other of said stations from using said line depend ent on the side of said line said positive potential is connected to.

10. In a telephone system, a partly line, two stations on said line, a common battery transmitter at each station adapted to be supplied with talking current over said party line from the exchange, means at one station eiiective to prevent current flowing over the line in one direction from passing through the associated transmitter, and means at the other station for preventing current flowing over the line in the other direction from passing through the associated transmitter.

11. In a telephone system, a party line, two stations on said line, a transmitter at each station adapted to be bridged across the line, a rectifier in series with one transmitter to responsive to the initiation of a call by a subscriber at either one of said stations for operating the associated line relay, and means dependent upon which line relay is operated for determining the section of the bank the call is to be extended over.

I11 witness whereof, I hereunto subscribe my name this 21st day of May, A. D. 1930. DAVID ADAM CHRISTIAN. In witness whereof, I hereunto subscribe my name this 21st day of May, A. D. 1930. EDMUND WILLIAM PALMER.

bar current flow from the line in a particular direction, and a rectifier in series with the other transmitter to bar current flow from the line in the opposite direction.

12. A telephone system as claimed in claim 11 in which two answering jacks are provided for the party line at the exchange, and a reversal in the line branch connected to one jack whereby transmitter current will be connected to the line in one direction on answering a call from one station and in the other direction on answering a call from the other station.

- 13. In a telephone system as claimed in claim 11, a line switch for extending the line responsive to a call from either station, and means responsive to a call for automatically connecting transmitter current to the line in one direction if one station is calling and in the other direction if the other station is calling.

14. In a telephone system, a party line, two stations on said line, a switch having two bank sections over which calls from said two stations are extended, respectively, means at each of said stations for starting the operation of said switch to extend a call, and means in said switch controlled by the station initiating a call for determining the bank section 60 over which the call is to be extended.

15. In a telephone system, a party line, two stations on said line, a switch having two line relays, one for each station, two bank sections for said switch over which calls from said 65 two stations are extended, respectively,means 

